Thanks to the matured technology and the popularization of the global positioning system (GPS), various kinds of satellite navigation devices have been developed and become a reliable and prerequisite guiding tool for drivers or travelers. By receiving positioning signals from at least three GPS satellites, the satellite navigation device may calculate its geographical coordinates. The navigation device may be used with an appropriate electronic map to provide the user with the information about the user's current position. Furthermore, when the user inputs a destination, the satellite navigation device may calculate based on the electronic map to plan out a path to the destination and guides the user to drive through the planned path.
However, the currently available civilian GPS is subject to limited accuracy. That is, the civilian GPS does not always provide highly precise positioning, and the positioning error varies with the user's current position and may range from several ten meters to several hundred meters. Therefore, particularly in cities, there are chances the satellite navigation device informs the user the destination is reached but the user fails to see the destination or is blocked by something on the way to the destination and gets lost. Besides, the satellite navigation device seems to be less useful when the user needs short-distance navigation aid.